pause on use card reg lwage educ pause reg lwage educ fatheduc pause reg lwage educ fatheduc age pause reg lwage educ fatheduc age IQ pause clear use bwght use bwght reg bwght cigs pause reg bwght cigs faminc pause reg bwght cigs motheduc fatheduc faminc pause clear use discrim reg psoda prpblck pause reg psoda prpblck crmrte pause reg psoda prpblck crmrte density pause reg psoda prpblck crmrte density income pause reg psoda prpblck crmrte density income nstores chain nregs nmgrs